A blog on fish biodiversity

Flame Hawkfish (Neocirrhites armatus)

This little fish was my dinner date on a recent night out. Though it turns out she has quite the complicated love life.

This is a flame hawkfish (Neocirrhites armatus), a small, tropical marine fish no bigger than a cosmetic compact mirror. That night dining out, I happened to be seated next to one of the restaurant’s saltwater aquariums.

I looked over, and our eyes met.

Native to the coral reefs of the western Pacific Ocean, the flame hawkfish is a sought-after species in the aquarium fish trade. Hobbyists enjoy its inquisitive nature, darting about the fish tank and peering at visitors with Muppet-like, googly eyes. Hawkfish are called such because of their habit of perching atop coral branches like hawks — then bursting off for circling swims to patrol their patch of territory, before returning to their favorite perching branch.

While our date that night was brief, the flame hawkfish has no shortage of romantic intrigue.

The flame hawkfish favors a specific type of coral and is highly preferential in terms of territory — some individuals have been observed to reside continuously on the same coral head for more than two years (Donaldson 1989).

Within their little homefront, flame hawkfish often live in monogamous pairs, defending their territory against intruding males and large females. Couples engage in frequent courtship year-round, and courtship takes place — you guessed it — around sunset (Donaldson 1989).

But like many other reef fish species, the “relationship status” of flame hawkfish has dizzying twists, many of them described by biologist Terry Donaldson in a 1989 study.

It seems that flame hawkfish monogamy depends on the size and number of their coral head habitat. On reefs where suitable coral heads are located sufficiently apart, flame hawkfish are likely to form monogamous pairs, presumably because the chance of males finding and meeting female mates is much lower.

But on coral heads large enough to support the territories of multiple females, or on reefs where suitable coral heads are located close enough together, males will “acquire” additional females — and a small harem forms.

Donaldson observed two of these relationship structures. In one, “a male living with a female often made visits to a second adjacent female during courtship periods, but returned to the coral where the first female resided.”

In another, a single male living alone will have visited “each of the females in adjacent coral heads during courtship periods but returned to its own coral head when courtship had been completed.”

To use American English vernacular, some male flame hawkfish, it would appear, are “playahs”.

But wait, there’s more! It turns out that flame hawkfish are “protogynous hermaphrodites” — all flame hawkfish are born female, but as they grow larger, their gonads will change from egg-producing ovaries into sperm-producing testes. The sex change is permanent and males can’t change back into females — although there are other species of hawkfish that can do so (Sadovy and Donaldson 1995).

This expected sex change might explain why on smaller coral heads where mates are hard to come by, flame hawkfish couples will chase away intruding males and and large females.

A resident female has an obvious incentive to chase away intruding females, to prevent them from stealing her man, so to speak. But a resident male has an incentive to chase away large females because a large female could be ready to change into a male — one that could subsequently steal his woman.

So, it was probably for the better that my hawkfish date didn’t get too serious. Even if we had hit it off, I might have come home one day to find all my possessions thrown out of my house, with my hawkfish bride-turned-groom possibly on the prowl and sleeping around with my neighbors. My life ruined because of some pint-sized, tomato-colored sleazeball…

“Who, me?” (Image Source: Oregon Coast Aquarium)

Addendum October 27, 2013:Professor Terry Donaldson followed up with me by email, and offered even more fascinating observations about the breeding ecology of the flame hawkfish. I asked him whether flame hawkfish changed sex simply as they grew larger, or whether females changed sex when a resident male is lost.

Donaldson replies: “I am still investigating the question you raised but can offer a bit of insight. With Neocirrhites and probably Oxycirrhites typus, both obligate coral-dwelling species, sex-change is probably driven by environmental/behavioral cues, e.g. the loss of the male in a mating group.”

Donaldson adds he suspects flame hawkfish are capable of bidirectional sex change — unlimited gender switches between male/female states — and he hopes to conduct further studies.

“Bidirectional sex change might occur also, but again this would be driven by a behavioral cue. If a larger male succeeds in gaining entry into a coral head, it might force the smaller resident male to change back into a female, so as to make the best of a bad situation without losing available microhabitat and mating opportunities.”